The Red Planet was once blue as one third of it was covered by a an ocean, American scientists claimed after analysing its surface using a new software.
The scientists from Northern Illinois University and the Lunar and Planetary Institute in Houston said they have managed to find dozens of valleys to build up the most detailed map of Mars to date.
The findings indicate the networks are more than twice as extensive as had been previously depicted in the only other planet-wide map of the valleys.
"All the evidence gathered by analysing the valley network on the new map points to a particular climate scenario on early Mars," NIU Geography Professor Wei Luo, said.
He added, "It would have included rainfall and the existence of an ocean covering most of the northern hemisphere, or about one-third of the planet's surface."
"The presence of more valleys indicates that it most likely rained on ancient Mars, while the global pattern showing this belt of valleys could be explained if there was a big northern ocean," he added.
Valley networks on Mars exhibit some resemblance to river systems on Earth, suggesting the Red Planet was once warmer and wetter than present -- a prospect greatly increases the chances of life having existed on the planet.
Scientists have previously hypothesized that a single ocean existed on ancient Mars, Journal of Geophysical Research -- Planets reported.